This project is concerned with 1) obtaining a detailed description of vocal behavior of squirrel monkeys, including the frequency of occurrence of defined microstructural features in a variety of behavioral contexts; 2) describing the developmental course of vocal behavior by serial recording during growth of laboratory-reared infants; 3) comparing the vocal behavior of captive monkeys of known and unknown social histories with vocal behavior in the natural state (via field studies in the Peruvian Amazon). Primary emphasis in FY 81 has been on studying the effect of the reproductive cycle on affiliative vocalizations in captive social groups. Two call types (one used by females, one by males) have been correlated with the estrous period, representing a significant new finding in the area of functional parcellation of the vocal repertoire of this species. Data collected in a 4-month field trip (Dr. Smith) support findings obtained in a captive group and reported last year.